How to Keep Textures High-Res Without Scaling UVs Ridiculously
Instead of directly connecting the UV Vector output from the UV Map node to the image input in the material nodes, insert a Vector > Mapping node. You can use it's scale component to scale the existing UVs, or move/rotate them.

For scaling only a Vector Math node set to multiply will do just as well.



This will obviously not work in an exported object for another program without corresponding material nodes.